This application is based on Japanese Patent Application No. 11-271063 filed Sep. 24, 1999.
1. Field of the Invention
The present invention is directed to a watercraft, and more particularly to a water preclusion and sound attenuation system employed in a watercraft engine induction system.
2. Description of the Related Art
Personal watercraft have become increasingly popular in recent years. This type of watercraft is sporting in nature; it turns swiftly, it is easily maneuverable, and accelerates quickly. A personal watercraft today commonly carries one rider and up to three passengers. Typically, the rider and passengers sit on a straddle-type seat that is formed by the hull of the watercraft. The straddle-type seat is generally aligned by the longitudinal axis of the hull.
The space beneath the straddle-type seat is usually used as an engine compartment for supporting the engine within the watercraft. The engine is preferably arranged within the engine compartment so that the crankshaft of the engine is aligned with the longitudinal axis of the watercraft. With the engine arranged as such, the crankshaft of the engine may be directly connected to an output shaft for driving a propulsion unit. Additionally, such an arrangement allows the engine to be arranged within the seat pedestal. Arranged as such, the engine and the seat pedestal form a compact unit. During operation, the rider and any passengers straddle the seat as well as the engine while they are seated on the straddle-type seat. With the hull shaped as such, the engine is in close spacing with the passengers during operation, thus allowing the overall size of the watercraft to remain quite small, resulting in a compact and highly maneuverable watercraft.
Although these watercraft are generally highly maneuverable and are used in a sporting manner, there is an interest in reducing the noise generated by this type of watercraft. One part of the watercraft propulsion system that can generate noise is the induction system of the engine. For the most part, the induction systems used for this type of watercraft have been designed primarily to ensure adequate air induction and at least some filtration of the inducted air. Little effort has been given, however, to the silencing of the induction system.
At least partially in response to the noise generated by two-cycle engines, which are commonly employed in personal watercraft, certain recreational facilities have banned the operation of two-cycle engine powered watercraft. Such bans have resulted in a decrease in popularity of personal watercraft powered by two-cycle engines.
Obviously, it is necessary for the induction system to be able to ingest an adequate flow of air for maximum engine performance. In many instances, the induction systems previously proposed for watercraft have not recognized the advantages of using a tuning arrangement on the intake side of the engine. One reason for this is that the space available in an engine compartment of a personal watercraft generally does not afford room for various types of intake tuning systems. Although it has been known that a large intake air box will prevent the generation of loud noises in the induction system and will generate a smooth flow of air into the combustion chambers, the small space available in the hulls of small watercraft have prevented the use of large air boxes.
For example, a large air box mounted so as to feed the intake runners arranged along one side of an engine within the engine compartment of a watercraft, will tend to attenuate induction noises. However, as discussed above, engines are preferably arranged within the engine compartments of personal watercraft such that their crankshaft is aligned with the longitudinal axis of the watercraft. As such, the intake runners open at a side of the engine, facing an inner wall of the seat pedestal. Therefore, the size of the intake air box affects the overall width of the engine. If a large intake air box is used, the overall width of the engine is increased.
Since the rider and any passengers straddle the seat pedestal and engine during operation, the overall width of the engine is limited to that which would fit within a straddle-type seat pedestal. If the pedestal is too wide, a rider cannot comfortably sit on the seat pedestal during operation of the watercraft. Therefore, any portions of the engine mounted along either side of the engine, such as the induction system, should be small enough such that the engine can still fit within the seat pedestal that defines an engine compartment of the watercraft.
Additionally, because of its sporting nature, personal watercraft are oftentimes laid on their side or are flipped over by advanced riders during use. It thus is also important that the induction system be designed in such a way to inhibit water, which may be present in the engine compartment, from passing into the engine through the induction system.
According to one aspect of the present invention, an engine induction system for a watercraft includes a first intake air chamber having an air inlet and communicating with the at least one combustion chamber and a second intake air chamber having an air inlet and an air outlet. A conduit connects the air inlet of the first intake air chamber to the outlet of the second intake air chamber. The outlet of the second intake air chamber is positioned vertically lower than the inlet of the first intake air chamber.
By positioning the outlet of the second intake air chamber vertically lower than the inlet of the first intake air chamber, the present induction system aids in preventing water from passing into the engine through the induction system. For example, as noted above, small watercraft, such as personal watercraft, are sporting in nature, and are oftentimes driven rigorously. Water can enter the engine compartment of these watercraft in several ways. In particular, water can enter the engine compartment through air vents that allow atmospheric air to enter the engine compartment so as to feed air to the engine for combustion. Water may also enter the engine compartment through leaks that may inadvertently occur. Finally, water may enter the engine compartment when an access opening of the engine compartment is open. Thus, when the watercraft is operated in a normal fashion, the water in the engine compartment can splash vigorously therein. However, by positioning the outlet of the second intake air chamber vertically lower than the inlet of the first intake air chamber, it is more difficult for such water to pass into the engine, where the damaging and corrosive effects of water can cause significant damage requiring expensive repairs.
According to another aspect of the present invention, an engine induction system for a watercraft includes a first intake air chamber having an air inlet and communicating with the at least one combustion chamber and a second intake air chamber having an air inlet and an air outlet. A conduit connects the air inlet of the first intake air chamber to the outlet of the second intake air chamber. The conduit is sized so as to form a third air chamber. Preferably, the cross-sectional flow area of the conduit is larger than the outlet of the second intake air chamber and the inlet of the first intake air chamber. As such, the present induction system causes air flowing therethrough to contract and expand several times before entering the engine. The expansion and contraction of the air flow through the induction system quiets and smoothes the air before it enters the engine.
According to another aspect of the present invention, an engine induction system for a watercraft includes a first intake air chamber having an air inlet and communicating with the at least one combustion chamber and a second intake air chamber having an air inlet and an air outlet. A conduit connects the air inlet of the first intake air chamber to the outlet of the second intake air chamber and a branched conduit extends upwardly from the conduit. As such, the branched conduit provides a water preclusive effect when the watercraft is capsized.
For example, as noted above, personal watercraft are oftentimes capsized during normal operation. Thus, water that may be present in the engine compartment of the watercraft can flow upstream through an air induction system as the watercraft rotates toward and reaches a capsized positioned. By providing an upwardly extending branched passage from the conduit, water that travels through the conduit when the watercraft is capsized, can flow into the branched passage. Additionally, when the watercraft is returned to an upright position, the water collected in the upwardly extending passage will drain back to the conduit, thus ejecting water that had previously flowed upstream into the induction system.
Further aspects, features and advantages of the present invention will become apparent from the detailed description of the preferred embodiment which follows.